some info on SCX's uranium interest for those interested.
NGALIA BASIN Uranium mineralisation was discovered in the vicinity of the Ngalia Basin (NT) in 1970 when a prospector employed by Central Pacific Minerals NL found radioactive gossanous material in a quartz vein in a granite of the adjacent Arunta Complex to the north of the basin. This prospect was later named Rankins Reward. Further ground prospecting located carnotite in outcrops of the Mount Eclipse Sandstone. The Bigrlyi deposit was discovered in 1973 by ground radiometric traversing and follow-up drilling. Uranium mineralisation was subsequently found in thirteen separate zones in the Mount Eclipse Sandstone (Fig. 35) (Ivanac & Spark, 1976; Fidler, Pope & Ivanac, 1990). In 1973, uranium mineralisation was discovered in Quaternary and Recent calcrete in the southern part of the basin. Regional geological setting
The Ngalia Basin is an elongate, intracratonic downwarp filled by Neoproterozoic and Palaeozoic strata. The basement rocks are highly deformed metamorphics, granites and sediments of the Palaeoproterozoic Arunta Block (Wygralak & Bajwah, 1998). Continental and marine strata of Neoproterozoic, Cambrian, Ordovician, Devonian and Carboniferous age comprise the Ngalia Basin sequence. The sequence has been divided into eleven formations with a maximum aggregate thickness of about 7500 m (Wells & Moss, 1983). Most formations are bounded by unconformities. The strata are mainly arenaceous, with interbedded dolomite and shale.
Uranium mineralisation is in the lower part of the Late Devonian to Late Carboniferous Mount Eclipse Sandstone. The host rocks are medium- to coarse-grained feldspathic sandstone with carbonate commonly forming a cement. The sandstones are mainly red, but restricted zones of light to dark grey are also present (Fidler & others, 1990). Minor amounts of shale, siltstone, conglomerate and dolomite are interbedded with the sandstone. The sandstone along the northern margin of the basin is thrust-faulted and folded.
Carnotite is the main ore mineral in the weathered sandstone, with uraninite in the primary zone. Carbonaceous material, including plant remains, is common in the reduced parts of the sandstone. Quaternary calcrete containing minor carnotite mineralisation has formed in the southern part of the basin where there is a broad area of lagoons, salt-pans and stream meanders related to the present drainage system.
Uranium mineralisation in the Ngalia Basin is closely associated with those parts of the Mount Eclipse Sandstone that contain carbonaceous detritus. Prior to diagenesis, run-off from the surrounding highlands permeated the sandstones and migrated into the sediments. In the oxidising environment these waters transported uranium and vanadium which were released from the basement rocks by weathering (Fidler & others, 1990). This uranium and vanadium precipitated in the reducing environment created by the presence of carbonaceous material and pyrite in the sandstones.
BIGRLYI DEPOSIT The Bigrlyi deposit is a series of discontinuous lenses that crop out over a strike length of 12.5 km in the lower part of the Mount Eclipse Sandstone along the northern margin of the Ngalia Basin (Ivanac & Spark, 1976; Wells & Moss, 1983). The host rock is a hard, medium-to-coarse arkosic sandstone, kaolinised in places and containing plant remains and other carbonaceous material. The sandstone sequence is folded, and dips vary from 75°S to 80°N (overturned). Mineralisation consists dominantly of uraninite and montroseite (VO(OH)), which changes to carnotite in the oxidised zones. Vanadium is present in amounts comparable to uranium, although the maximum levels of each element rarely coincide (Fidler & others, 1990). The uranium mineralisation is in radioactive disequilibrium. Gangue minerals are dominantly quartz with very minor orthoclase, kaolin, muscovite, chlorite and calcite. Detailed drilling has outlined resources in eight separate lenses. Central Pacific Minerals NL (1982) reported 2181 t U3O8 proved resources, averaging 0.372%; 486 t U3O8 probable resources, averaging 0.252%; and 107 t U3O8 possible resources, averaging 0.361%.
